In exhaust systems of internal combustion engines, there are disposed exhaust purifying apparatus such as a catalytic converter, a diesel particulate trapping apparatus and an NOx occluding-purifying apparatus. FIG. 1 is a cross-sectional view showing an example of a catalytic converter 10 which is an example of these exhaust purifying apparatus. In this catalytic converter 10, an introduction pipe 16 through which exhaust gas discharged from an internal combustion engine is introduced is connected to one end of a metal casing 11, and a discharge pipe 17 through which the exhaust gas which has passed through a catalyst carrier 12 is discharged outside is attached to the other end thereof. Further, the catalyst carrier 12 is provided inside the metal casing 11 with the intervention of a holding material 13 for a catalyst converter. Furthermore, an electric heater and a temperature sensor for burning particulates accumulated in the catalyst carrier, namely a honeycomb filter, to recover a filtering function (also referred to as regeneration treatment) may be provided on an exhaust gas introduction side (also referred to as a suction side) with respect to a catalyst carrier, and another pipe for feeding combustion air may be connected thereto, although not shown in the figure. According to such constitution, when the amount of the particulates accumulated in the catalyst carrier 12 increases to result in an increase in pressure drop, the regeneration treatment can be conducted.
The metal casing 11 can be constituted as to divide a cylindrical body into two parts along a longitudinal direction thereof, as shown in FIG. 2. The catalyst carrier 12 around which the holding material 13 for a catalyst converter has been wound is located at a predetermined position in a lower shell 22b, and an upper shell 22a is placed on the lower shell 22b so that a through hole 23a formed in an upper fixing portion 23 is exactly superimposed on a through hole 24a formed in a lower fixing portion 24. A bolt 25 is inserted through the through holes 23a and 24a, and fixed by a nut or the like. Alternatively, the upper fixing portion 23 and the lower fixing portion 24 may be welded with each other. Further, the metal casing 11 may be a cylindrical body 50 as shown in FIG. 3. Although this requires no assembling work necessary for the metal casing having the two-divided structure as shown in FIG. 2, it is necessary to press the catalyst carrier 12 around which the holding material 13 for a catalytic converter has been wound into the cylindrical body from an opening 51 thereof.
The holding material 13 for a catalytic converter is required to hold the catalyst carrier 12 and to block a gap between the metal casing 11 and the catalyst carrier 12. For example, holding force has been enhanced by forming high-density sites higher in density than the other sites in a stripe shape throughout the length along the axial direction of the catalyst carrier (see JP-A-1-247711) or forming high-density sites along the circular shape in a circumferential direction of the catalyst carrier (see JP-A-2003-262117).